In the semiconductor industry, singulation or dicing devices are used for cutting semiconductor wafers or packaged semiconductor devices along a lattice of cutting lines. The cutting lines define boundaries between individual electronic devices on a semiconductor wafer. Dicing is also known as singulation or die cutting. A singulation device includes a number of components including a chuck device having a support surface for holding a workpiece being cut, and a cutting blade including a spindle and a blade rotatably mounted on the spindle.
It is important to control and maintain an accurate cutting depth of the workpiece by the cutting blade—if the cutting blade is spaced further away from the workpiece than anticipated, the workpiece would be insufficiently cut by the cutting blade due to an insufficient cutting depth; on the other hand, if the cutting blade is spaced nearer to the workpiece than anticipated, the chuck device would be damaged by the cutting blade. More specifically, the positional accuracy of the cutting blade should be in the range of a few microns to ensure precision of the singulation process. There are however various factors affecting a separation distance between the cutting blade and the chuck device (and thereby the workpiece) which might in turn affect the cutting depth of the workpiece by the cutting blade—first, dynamic positional changes of the components of the singulation device; and second, wearing of the cutting blade due to continuous use. Thus, it is desirable to periodically determine the separation distance between the cutting blade and the workpiece to ensure an accurate cutting depth of the workpiece, prior to the workpiece being cut.
Conventionally, non-contact methods are used to determine the separation distance between the cutting blade and the workpiece. One example of such non-contact methods may include: i) a collimated light emitter for emitting light; ii) a collimated light receiver for receiving the light from the collimated light emitter; and iii) mirrors for reflecting the light from the collimated light emitter to the collimated light receiver. In particular, the light from the collimated light emitter converges midway between the mirrors at a point below a cutting tip of the cutting blade and above the chuck device. During detection, the cutting blade moves downwards slowly until the tip of the cutting blade just crosses the position where the light from the collimated light emitter is converged by the mirrors. At this point, the collimated light receiver detects a reduction in the amount of light received—which allows the position of the tip of the cutting blade relative to the chuck device and, accordingly, the separation distance between the tip of the cutting blade and the workpiece to be determined.
One major disadvantage of the above non-cutting method is the slowness in measuring the position of the cutting blade, which reduces the production efficiency (or units-per-hour, UPH) of the singulation device. In order to obtain measurements with accuracy in the range of a few microns, it is necessary for the cutting blade to move very slowly towards the light-converging point. If the cutting blade advances too fast, the tip of the cutting blade will overshoot beyond the light-converging point, thereby causing the measurement to be inaccurate.
In addition, the measurement process ought to be repeated to ensure repeatability—and thus reliability—of earlier measurement(s). Thus the entire duration usually takes around 20-30 seconds, which significantly reduces the production efficiency of the singulation device. As the unit size of electronic devices in a wafer or a package strip becomes smaller with advancing technology, it is common to perform around 5-10 cycles of measurements per package strip to ensure repeatability of the results. Consequently, the entire duration for the above non-contact method to obtain measurements is further lengthened, thus exacerbating the reduction of the production efficiency of the singulation device.
Thus it is an object of the present invention to propose a singulation apparatus that ameliorates the limitation of the above conventional non-contact method.